Zic2 abrogates an alternative Wnt signaling pathway to convert axon attraction into repulsion

ABSTRACTWnt signaling is involved in axon pathfinding during brain wiring but it is unknown how Wnt ligands promote attraction or repulsion. In addition, the participation of the canonical (βcatenin-dependent transcription) versus non-canonical (βcatenin-independent) Wnt pathways in this process remains controversial. Here we show that Wnt5a is expressed at the optic chiasm midline and promotes axon crossing by triggering an alternative Wnt pathway that depends on polarized accumulation of βcatenin at the axon terminal but does not activate the canonical pathway. Remarkably, this alternative pathway is silenced by the transcription factor Zic2 in the small subset of ipsilaterally projecting neurons. Zic2 directly regulates genes related to Wnt and Eph signaling that lead to global accumulation of βcatenin but triggers its asymmetric phosphorylation to facilitate the steering of the growth cone. This alternative Wnt pathway found in contralateral axons and its Zic2-mediated abrogation in ipsilateral neurons is likely operating in many other contexts requiring a two-way response to Wnt ligands.

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R-Spondin Family Members Regulate the Wnt Pathway by a Common Mechanism

Molecular Biology of the Cell ◽

10.1091/mbc.e08-02-0187 ◽

2008 ◽

Vol 19 (6) ◽

pp. 2588-2596 ◽

Cited By ~ 200

Author(s):

Kyung-Ah Kim ◽

Marie Wagle ◽

Karolyn Tran ◽

Xiaoming Zhan ◽

Melissa A. Dixon ◽

...

Keyword(s):

Wnt Signaling ◽

Wnt Pathway ◽

Expression Patterns ◽

Family Members ◽

Wnt Signaling Pathway ◽

Direct Consequence ◽

Common Mechanism ◽

Wnt Ligands ◽

Canonical Wnt

The R-Spondin (RSpo) family of secreted proteins is implicated in the activation of the Wnt signaling pathway. Despite the high structural homology between the four members, expression patterns and phenotypes in knockout mice have demonstrated striking differences. Here we dissected and compared the molecular and cellular function of all RSpo family members. Although all four RSpo proteins activate the canonical Wnt pathway, RSpo2 and 3 are more potent than RSpo1, whereas RSpo4 is relatively inactive. All RSpo members require Wnt ligands and LRP6 for activity and amplify signaling of Wnt3A, Wnt1, and Wnt7A, suggesting that RSpo proteins are general regulators of canonical Wnt signaling. Like RSpo1, RSpo2-4 antagonize DKK1 activity by interfering with DKK1 mediated LRP6 and Kremen association. Analysis of RSpo deletion mutants indicates that the cysteine-rich furin domains are sufficient and essential for the amplification of Wnt signaling and inhibition of DKK1, suggesting that Wnt amplification by RSpo proteins may be a direct consequence of DKK1 inhibition. Together, these findings indicate that RSpo proteins modulate the Wnt pathway by a common mechanism and suggest that coexpression with specific Wnt ligands and DKK1 may determine their biological specificity in vivo.

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Regulation of Wnt Signaling by FOX Transcription Factors in Cancer

Cancers ◽

10.3390/cancers13143446 ◽

2021 ◽

Vol 13 (14) ◽

pp. 3446

Author(s):

Stefan Koch

Keyword(s):

Transcription Factors ◽

Wnt Signaling ◽

Wnt Pathway ◽

Treatment Options ◽

Wnt Signaling Pathway ◽

Tissue Homeostasis ◽

Fine Tuning ◽

Dependent Manner ◽

Forkhead Box ◽

Signaling Activity

Aberrant activation of the oncogenic Wnt signaling pathway is a hallmark of numerous types of cancer. However, in many cases, it is unclear how a chronically high Wnt signaling tone is maintained in the absence of activating pathway mutations. Forkhead box (FOX) family transcription factors are key regulators of embryonic development and tissue homeostasis, and there is mounting evidence that they act in part by fine-tuning the Wnt signaling output in a tissue-specific and context-dependent manner. Here, I review the diverse ways in which FOX transcription factors interact with the Wnt pathway, and how the ectopic reactivation of FOX proteins may affect Wnt signaling activity in various types of cancer. Many FOX transcription factors are partially functionally redundant and exhibit a highly restricted expression pattern, especially in adults. Thus, precision targeting of individual FOX proteins may lead to safe treatment options for Wnt-dependent cancers.

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Wnt Signaling in Vascular Calcification

Frontiers in Cardiovascular Medicine ◽

10.3389/fcvm.2021.708470 ◽

2021 ◽

Vol 8 ◽

Author(s):

Kaylee Bundy ◽

Jada Boone ◽

C. LaShan Simpson

Keyword(s):

Cardiovascular Disease ◽

Wnt Signaling ◽

Signaling Pathway ◽

Vascular Calcification ◽

Arterial Wall ◽

Wnt Signaling Pathway ◽

Phenotypic Switch ◽

Wnt Ligands ◽

And Function ◽

Canonical Wnt

Cardiovascular disease is a worldwide epidemic and considered the leading cause of death globally. Due to its high mortality rates, it is imperative to study the underlying causes and mechanisms of the disease. Vascular calcification, or the buildup of hydroxyapatite within the arterial wall, is one of the greatest contributors to cardiovascular disease. Medial vascular calcification is a predictor of cardiovascular events such as, but not limited to, hypertension, stiffness, and even heart failure. Vascular smooth muscle cells (VSMCs), which line the arterial wall and function to maintain blood pressure, are hypothesized to undergo a phenotypic switch into bone-forming cells during calcification, mimicking the manner by which mesenchymal stem cells differentiate into osteoblast cells throughout osteogenesis. RunX2, a transcription factor necessary for osteoblast differentiation and a target gene of the Wnt signaling pathway, has also shown to be upregulated when calcification is present, implicating that the Wnt cascade may be a key player in the transdifferentiation of VSMCs. It is important to note that the phenotypic switch of VSMCs from a healthy, contractile state to a proliferative, synthetic state is necessary in response to the vascular injury surrounding calcification. The lingering question, however, is if VSMCs acquire this synthetic phenotype through the Wnt pathway, how and why does this signaling occur? This review seeks to highlight the potential role of the canonical Wnt signaling pathway within vascular calcification based on several studies and further discuss the Wnt ligands that specifically aid in VSMC transdifferentiation.

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A Wnt signaling pathway controls hox gene expression and neuroblast migration in C. elegans

Development ◽

10.1242/dev.126.1.37 ◽

1999 ◽

Vol 126 (1) ◽

pp. 37-49 ◽

Cited By ~ 9

Author(s):

J.N. Maloof ◽

J. Whangbo ◽

J.M. Harris ◽

G.D. Jongeward ◽

C. Kenyon

Keyword(s):

Gene Expression ◽

Wnt Signaling ◽

Wnt Pathway ◽

Hox Genes ◽

Wnt Signaling Pathway ◽

Beta Catenin ◽

Hox Gene ◽

C Elegans ◽

Neuroblast Migration ◽

Pathway Gene

The specification of body pattern along the anteroposterior (A/P) body axis is achieved largely by the actions of conserved clusters of Hox genes. Limiting expression of these genes to localized regional domains and controlling the precise patterns of expression within those domains is critically important for normal patterning. Here we report that egl-20, a C. elegans gene required to activate expression of the Hox gene mab-5 in the migratory neuroblast QL, encodes a member of the Wnt family of secreted glycoproteins. We have found that a second Wnt pathway gene, bar-1, which encodes a beta-catenin/Armadillo-like protein, is also required for activation of mab-5 expression in QL. In addition, we describe the gene pry-1, which is required to limit expression of the Hox genes lin-39, mab-5 and egl-5 to their correct local domains. We find that egl-20, pry-1 and bar-1 all function in a linear genetic pathway with conserved Wnt signaling components, suggesting that a conserved Wnt pathway activates expression of mab-5 in the migratory neuroblast QL. Moreover, we find that members of this Wnt signaling system play a major role in both the general and fine-scale control of Hox gene expression in other cell types along the A/P axis.

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Wnt Production in Dental Epithelium Is Crucial for Tooth Differentiation

Journal of Dental Research ◽

10.1177/0022034519835194 ◽

2019 ◽

Vol 98 (5) ◽

pp. 580-588 ◽

Cited By ~ 5

Author(s):

Y. Xiong ◽

Y. Fang ◽

Y. Qian ◽

Y. Liu ◽

X. Yang ◽

...

Keyword(s):

Wnt Signaling ◽

Signaling Pathway ◽

Tooth Development ◽

Wnt Signaling Pathway ◽

Conditional Knockout ◽

Canonical Wnt Signaling ◽

Odontoblast Differentiation ◽

Wnt Ligands ◽

Dental Epithelium ◽

Canonical Wnt

The Wnt ligands display varied spatiotemporal expression in the epithelium and mesenchyme in the developing tooth. Thus far, the actions of these differentially expressed Wnt ligands on tooth development are not clear. Shh expression specifies the odontogenic epithelium during initiation and is consistently restricted to the dental epithelium during tooth development. In this study, we inactivate Wntless ( Wls), the key regulator for Wnt trafficking, by Shh-Cre to investigate how the Wnt ligands produced in the dental epithelium lineage act on tooth development. We find that conditional knockout of Wls by Shh-Cre leads to defective ameloblast and odontoblast differentiation. WlsShh-Cre teeth display reduced canonical Wnt signaling activity in the inner enamel epithelium and the underlying mesenchyme at the early bell stage, as exhibited by target gene expression and BAT-gal staining. The expression of Wnt5a and Wnt10b is not changed in WlsShh-Cre teeth. By contrast, Wnt10a expression is significantly increased in response to epithelial Wls deficiency. In addition, the expression of Hedgehog signaling pathway components Shh, Gli1, and Patched1 was greatly decreased in WlsShh-Cre teeth. Epithelial Wls loss of function in Shh lineage also leads to aberrant cell proliferation in dental epithelium and mesenchyme at embryonic day 16.5; however, the cell apoptosis is unaffected. Moreover, we find that Decorin and Col1a1, the key markers for odontoblast differentiation that are downregulated in WlsShh-Cre teeth, act as direct downstream targets of the canonical Wnt signaling pathway by chromatin immunoprecipitation analysis. Additionally, Decorin and Col1a1 expression can be increased by lithium chloride (LiCl) treatment in the in vitro tooth explants. Taken together, our results suggest that the spatial expression of Wnt ligands within the dental epithelial lineage regulates the differentiation of tooth structures in later stages.

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R-spondins can potentiate WNT signaling without LGRs

eLife ◽

10.7554/elife.33126 ◽

2018 ◽

Vol 7 ◽

Cited By ~ 48

Author(s):

Andres M Lebensohn ◽

Rajat Rohatgi

Keyword(s):

Wnt Signaling ◽

Wnt Signaling Pathway ◽

Heparan Sulfate Proteoglycans ◽

G Protein Coupled Receptors ◽

Leucine Rich Repeat ◽

Biological Functions ◽

High Affinity ◽

Wnt Ligands ◽

Necessary And Sufficient ◽

G Protein Coupled

The WNT signaling pathway regulates patterning and morphogenesis during development and promotes tissue renewal and regeneration in adults. The R-spondin (RSPO) family of four secreted proteins, RSPO1-4, amplifies target cell sensitivity to WNT ligands by increasing WNT receptor levels. Leucine-rich repeat-containing G-protein coupled receptors (LGRs) 4-6 are considered obligate high-affinity receptors for RSPOs. We discovered that RSPO2 and RSPO3, but not RSPO1 or RSPO4, can potentiate WNT/β-catenin signaling in the absence of all three LGRs. By mapping the domains on RSPO3 that are necessary and sufficient for this activity, we show that the requirement for LGRs is dictated by the interaction between RSPOs and the ZNRF3/RNF43 E3 ubiquitin ligases and that LGR-independent signaling depends on heparan sulfate proteoglycans (HSPGs). We propose that RSPOs can potentiate WNT signals through distinct mechanisms that differ in their use of either LGRs or HSPGs, with implications for understanding their biological functions.

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Replicating Adenoviruses That Target Tumors with Constitutive Activation of the wnt Signaling Pathway

Journal of Virology ◽

10.1128/jvi.75.6.2857-2865.2001 ◽

2001 ◽

Vol 75 (6) ◽

pp. 2857-2865 ◽

Cited By ~ 51

Author(s):

Michele Brunori ◽

Maddalena Malerba ◽

Haruhiko Kashiwazaki ◽

Richard Iggo

Keyword(s):

Wnt Signaling ◽

Cancer Cells ◽

Wnt Pathway ◽

Wnt Signaling Pathway ◽

Lung Model ◽

Colorectal Tumors ◽

Colon Tumors ◽

Treat All

ABSTRACT Despite important advances in understanding the molecular basis of cancer, few treatments have been devised which rationally target known causal oncogenic defects. Selectively replicating viruses have a major advantage over nonreplicating viruses to target these defects because the therapeutic effect of the injected virus is augmented by virus produced within the tumor. To permit rational targeting of colon tumors, we have developed replicating adenoviruses that express the viral E1B and E2 genes from promoters controlled by the Tcf4 transcription factor. Tcf4 is constitutively activated by mutations in the adenomatous polyposis coli and β-catenin genes in virtually all colon tumors and is constitutively repressed by Groucho and CtBP in normal tissue. The Tcf-E2 and Tcf-E1B promoters are active in many, but not all, cell lines with activation of the wnt pathway. Viruses with Tcf regulation of E2 expression replicate normally in SW480 colon cancer cells but show a 50- to 100-fold decrease in replication in H1299 lung cancer cells and WI38 normal fibroblasts. Activation of wnt signaling by transduction of a stable β-catenin mutant into normal fibroblasts renders the cells permissive for virus replication. Insertion of Tcf4 sites in the E1B promoter has only small effects on replication in vitro but significantly reduces the inflammatory response in a rodent lung model in vivo. Replicating adenoviruses with Tcf regulation of both E1B and E2 transcription are potentially useful for the treatment of liver metastases from colorectal tumors, but additional changes will be required to produce a virus that can be used to treat all colon tumors.

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Inhibition of Wnt Pathway Signaling by Thalidomide and Revlimid: Studies in a Drosophila Model System.

Blood ◽

10.1182/blood.v104.11.3356.3356 ◽

2004 ◽

Vol 104 (11) ◽

pp. 3356-3356

Author(s):

A. Keith Stewart ◽

Yuan Xiao Zhu ◽

Maryan Yahyapour ◽

Armen Manoukian ◽

Sam E. Scanga

Keyword(s):

Wnt Signaling ◽

Cell Lines ◽

Wnt Pathway ◽

High Throughput Sequencing ◽

Cellular Proliferation ◽

Wnt Signaling Pathway ◽

Myeloma Cell ◽

Lacz Expression ◽

Western Blots ◽

Drosophila Model

Abstract High throughput sequencing, gene expression profiling and protein biochemistry in myeloma have all consistently revealed elevated expression of wnt signaling pathways in malignant plasma cells. Indeed, downregulation of the Wnt pathway in myeloma cells has recently been shown to inhibit myeloma cellular proliferation. Preliminary pharmacogenomic studies have also suggested that hyperactivation of the wnt signaling antagonist DKK-1 is associated with response to the immunomodulators thalidomide and revlimid. The mechanism of action for these therapeutically active drugs is however by no means clear as multiple biologic consequences of treatment have been proposed. We report here use of a drosophila model to examine wnt signaling inhibition by these pharmaceuticals. We employed a unique drosophila larval imaginal disc culture system in which wnt pathway activity is monitored through control of LacZ expression by the distalless promoter. In this system 10uM of both thalidomide and revlimid reproducibly inhibit lacZ expression when compared with vehicle controls. Western blots of larva confirmed downregulation of expression of armadillo (the drosophila b-catenin homologue) by both drugs but particularly revlimid. Lithium Chloride is an inhibitor of the drosphila GSK3b homologue shaggy and thus mimics wnt signaling by stabilizing b-catenin. The effect of Lithium could not be overcome by thalidomide or revlimid indicating that the action of these drugs is upstream of shaggy (or GSK3). Next we employed a fly transgenic for wingless which is embryonic lethal. By adding either drug to larval culture medium the lethality of wingless expression was reversed. Indeed drosophila embryos fed thalidomide exhibited developmental plate abnormalities. We next sought evidence that similar effects were evident in revlimid treated human myeloma. As previously reported most myeloma cell lines studied expressed b-catenin and this protein was downregulated by revlimid treatment of human myeloma cell lines co-incident with inhibition of growth as measured by MTT assay. We sought, but failed to find evidence of up-regulation of the wnt signaling pathway antagonist DKK-1 using an ELISA assay on pre and post treatment serum samples in patients responding to thalidomide.The implications of wnt signaling inhibition as a primary or secondary readout of therapeutic efficiency in MM may be of substantial importance in subsequent design of drug therapies or combination therapies.

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Activation of Non-Canonical Wnt Pathway in Human Mesenchymal Cells Affects Osteogenic Differentiation: A Potential Target in Multiple Myeloma Microenvironment

Blood ◽

10.1182/blood.v112.11.2742.2742 ◽

2008 ◽

Vol 112 (11) ◽

pp. 2742-2742 ◽

Cited By ~ 1

Author(s):

Nicola Giuliani ◽

Simona Colla ◽

Paola Storti ◽

Gaetano Donofrio ◽

Marina Bolzoni ◽

...

Keyword(s):

Alkaline Phosphatase ◽

Wnt Signaling ◽

Osteogenic Differentiation ◽

Wnt Signaling Pathway ◽

Inhibitory Effect ◽

Canonical Wnt Signaling ◽

Wnt Pathways ◽

Canonical Wnt ◽

Wnt Signal ◽

Alkaline Phosphatase Expression

Abstract Osteoblast suppression is the hallmark of Multiple Myeloma (MM) osteolytic bone lesions mainly due to the capacity of MM cells to inhibit the osteogenic differentiation of bone marrow (BM) mesenchymal cells (MSC). Many evidences suggest that Wnt signaling is critically involved in the regulation of osteoblast formation. Recently, in murine osteoprogenitor cells and in MM mouse models it has been shown that activation of canonical Wnt pathway stimulate osteoblast formation and blunts MM-induced bone destruction. In this study we have investigated whether modulation of both canonical and noncanonical Wnt signaling pathway may affect osteogenic differentiation of human MSC and counterbalance the suppressive effect of MM cells. First we checked the potential expression of Wnt activators and inhibitors by human MSC and osteoprogenitor cells (PreOB) by gene arrays. We found that both cells expressed the activator of non-canonical Wnt pathways Wnt5a but lack of express the main activators of canonical Wnt signaling as Wnt1, Wnt3a and Wnt8. The presence of the Wnt5a receptor FZD2 and FZD5 was also detected in both cells as well as that of FZD3, FZD6 and FDZ7 and the Wnt canonical co-receptors LRP5 and LRP6. On the other hand we found that both inhibitors of canonical and non-canonical Wnt pathways DKK-1 and sFRP-1 were expressed by MSC. Secondly, activation of either canonical or non-canonical Wnt signaling pathway by Wnt3a and Wnt5a treatment respectively was performed in human MSC to evaluate the effect on osteogenic differentiation and the expression of osteoblast related markers (Collagen I, Osteocalcin and Alkaline Phosphatase). We found that Wnt5a treatment but not Wnt3a significantly increased the early osteogenic differentiation and the expression of alkaline phosphatase in MSC. Consistently in a co-culture system with MM cells Wnt5a treatment blunted, at least in part, the inhibitory effect of MM cells on alkaline phosphatase expression by MSC and PreOB. To go further inside, we evaluated in both primary human BM MSC and the human MSC cell line HS-5 the effect of either the activation of non-canonical Wnt signaling by Wnt5a overexpression using a lentivirus vector or the Wnt5a suppression using siRNA. Wnt5a over-expression in MSC induced the activation of Wnt/Ca++ non-canonical pathway as demonstrated by the increase of Wnt5a secretion and phospho-PKC expression detected by westernblot analysis. Consequently to non-canonical Wnt signal activation we found a significant increase of alkaline phosphatase expression by MSC cells as well as of their osteogenic differentiation. Interestingly, analyzing the gene expression profile by microarray, we found that Wnt5a overexpression in MSC also affects the expression of chemokines, inflammatory cytokines and pro-angiogenic molecules. In conclusion our data indicate that activation of non-canonical Wnt signal pathway may represent a potential target in MM microenvironment to counterbalance the inhibitory effect of MM cells on osteogenic differentiation of human MSC.

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Wnt/β-Catenin/Tcf Signaling Induces the Transcription of Axin2, a Negative Regulator of the Signaling Pathway

Molecular and Cellular Biology ◽

10.1128/mcb.22.4.1172-1183.2002 ◽

2002 ◽

Vol 22 (4) ◽

pp. 1172-1183 ◽

Cited By ~ 1080

Author(s):

Eek-hoon Jho ◽

Tong Zhang ◽

Claire Domon ◽

Choun-Ki Joo ◽

Jean-Noel Freund ◽

...

Keyword(s):

Wnt Signaling ◽

Signaling Pathway ◽

Wnt Pathway ◽

Genomic Sequence ◽

Wnt Signaling Pathway ◽

Genomic Region ◽

Negative Regulator ◽

Mobility Shift ◽

Specific Expression

ABSTRACT Axin2/Conductin/Axil and its ortholog Axin are negative regulators of the Wnt signaling pathway, which promote the phosphorylation and degradation of β-catenin. While Axin is expressed ubiquitously, Axin2 mRNA was seen in a restricted pattern during mouse embryogenesis and organogenesis. Because many sites of Axin2 expression overlapped with those of several Wnt genes, we tested whether Axin2 was induced by Wnt signaling. Endogenous Axin2 mRNA and protein expression could be rapidly induced by activation of the Wnt pathway, and Axin2 reporter constructs, containing a 5.6-kb DNA fragment including the promoter and first intron, were also induced. This genomic region contains eight Tcf/LEF consensus binding sites, five of which are located within longer, highly conserved noncoding sequences. The mutation or deletion of these Tcf/LEF sites greatly diminished induction by β-catenin, and mutation of the Tcf/LEF site T2 abolished protein binding in an electrophoretic mobility shift assay. These results strongly suggest that Axin2 is a direct target of the Wnt pathway, mediated through Tcf/LEF factors. The 5.6-kb genomic sequence was sufficient to direct the tissue-specific expression of d2EGFP in transgenic embryos, consistent with a role for the Tcf/LEF sites and surrounding conserved sequences in the in vivo expression pattern of Axin2. Our results suggest that Axin2 participates in a negative feedback loop, which could serve to limit the duration or intensity of a Wnt-initiated signal.

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